Indirect product heating, for example in Ultra-High Temperature (UHT) systems by a heat exchange on a wall can take place both with so-called plate heat exchanger systems or also, as in the description herein, with so-called tube bundle heat exchangers, in which thermal energy is transferred by the tube walls of a group of inner tubes. The food product to be treated thereby flows in the inner tubes, while a heat carrier medium, in general water or vapor, flows in the annular gap space of the casing tube, which surrounds the parallel-connected inner tube. This type of tube bundle heat exchanger is known from DE 94 03 913 U1.
Particularly temperature-sensitive products, like for example desserts, sauces or concentrates, in particular with a high viscosity and, if applicable, with solid-containing components like entire pieces, pulp or fibers, require an exact and quick temperature adjustment of the product for the required temperature conditions. Moreover, a thermally or mechanically gentle treatment of the product is simultaneously required. It follows from the requirement for a thermally gentle treatment that all partial quantities of a product to be subjected to heat treatment pass through the same required temperature level progression at the same time and over the same period of time. In other words, this means that all partial quantities are subject to the same thermal and flow-mechanical conditions at the same retention time.
Mechanically gentle treatment means that the mechanical load of the product is held as low as possible. This type of load always occurs in particular when the product is subject to shear forces. The latter notoriously occur during deflections, discontinuous cross-sectional transitions, branchings and mergings of the flow ducts.
DE 103 11 529 B3 addresses the branching problem of the flow in the inlet area of the tube bundle plate of a tube bundle heat exchanger (e.g., DE 94 03 913 U1), as preferably used in UHT systems. The targeted measures suggested under the conceptual formulation specified there relate exclusively to the branching of a product into inner tubes of the tube bundle heat exchanger receiving a number of partial quantities of this product, wherein among other things a displacement body is provided, which is arranged axially symmetrically and concentrically to the tube carrier plate. This thus relates exclusively to an apparatus for influencing the inflow region of a tube carrier plate of a tube bundle heat exchanger in question. The inner tubes are thereby distributed over the entire circular area of the tube carrier plate, generally on more than one pitch circle, exclusively of a narrowly restricted central region. Under these prerequisites, there are, from the outset both in the inlet as well as in the outflow region of the respective tube carrier plate, thus during the branching and the merging of the flow, flow paths with different lengths to the inlet into the inner tubes or respectively from the outlet out of them. For this reason alone, different retention times result for the partial quantities of the product flowing through the respective inner tubes.
As shown in the description of DE 103 11 529 B3, the cross-section-like design of the tube bundle heat exchanger generally takes place such that the average flow speed in the inner tube is also present in a connection bend, which is connected on one side with a fixed-bearing-side exchanger flange and on the other side indirectly with a loose-bearing-side connecting piece permanently connected with a loose-bearing-side tube carrier plate. The flow mechanical design of the flow pull between the connection bend and the inlet into the inner tubes in the fixed-bearing-side tube carrier plate is defined by the following characteristics. Namely, the flow supplied via the connection bend with the average flow speed is accelerated in an annular gap cross-section narrowed in a nozzle-like manner, which is formed between the displacement body and the fixed-bearing-side exchanger flange. The resulting flow speed reaches its maximum flow speed in a minimum annular gap cross-section (narrowest point of the annular gap cross-section). Behind the narrowest point of the annular gap cross-section, the latter extends as a result of an extending passage cross-section because this extension cannot be compensated to the same degree by a front part of the displacement body, which expands in the inflow direction. The flow thus experiences a delay behind the narrowest point of the annular gap cross-section. The flow breaks away as expected at a flow break point at, for example, the greatest outside diameter of the front part of the displacement body. Behind the flow break point, the cross-section of the displacement body is reduced in a rear part continuously down to a minimum cross-section of a shaft, so that a continuously expanding passage cross-section is available for the flow in cooperation with the expanding passage cross-section. The flow is thus further delayed in the region of the rear part of the displacement body until it enters the inner tubes with the average flow speed.
In order to solve the problem described above of different retention times during the branching and merging of the flow, WO 2011/085784 A2 suggests arranging all inner tubes of the tube bundle in a circular-ring-shaped manner on a single circle and in an outer channel of the tube bundle heat exchanger designed as an annular space. The inner tubes, flowed through in parallel, extend in the longitudinal direction of the outer channel and are each supported on the end side in a tube carrier plate.
This arrangement of the inner tubes is combined with respectively one axially symmetrical displacement body permanently arranged concentrically on the tube carrier plate at the inlet and the outlet of the product. The respective displacement body reaches centrally through an exchanger flange associated with the tube carrier plate, wherein the exchanger flange has a connection opening on its side facing away from the associated tube carrier plate, which preferably opens axially symmetrically via a transition, preferably designed in a conical or cone-shaped manner, free in particular of points of discontinuities up to an extended passage cross-section provided on the end side. With an inner contour formed by the connection opening, the conical or cone-shaped transition and the extended passage cross-section, the respective displacement body forms an annular space-like channel, which extends continuously from the connection opening to the tube carrier plate in its respective annular gap cross-section. The end-side areas of the known tube bundle heat exchanger are each designed as mirror images of each other and with the same dimensions, at least respectively in connection with the outer channel, wherein this symmetry also expressly includes the two displacement bodies and the two annular space-like channels.
Almost congruent flow paths and mainly uniform heat transfer conditions thereby result in all relevant areas of the tube bundle heat exchanger for all partial quantities of the product branching and merging into the inner tubes between the product inlet and outlet.
However, congruent flow paths do not simultaneously mean that the flow pulls of the individual partial quantities are constructed with an unchanged flow speed, which avoids acceleration or respectively delay. As shown in the description of WO 2011/085784 A2, a first annular channel in the first exchanger flange (region of the product inlet; inlet side) and a second annular channel in the second exchanger flange (region of the product outlet; outlet side) and thus the associated flow speeds change respectively continuously and bounce-free. As a result, each of the partial quantities branched on the outlet side flow out of the inner tubes of the second tube carrier plate into a second inlet groove with a third flow speed. A delay to a minimum value of the unbranched flow then takes places in the course of the merging of the partial quantities in the largest annular gap cross-section of this second inlet groove, a second flow speed, and the unbranched flow is finally accelerated in the annular second channel to a first flow speed in the second connection opening.